The present invention relates to a device for establishing proper femoral component rotation in, for example, knee replacement surgery, and more particularly to a device for locating the anteroposterior femoral axis and for locating a line parallel or substantially parallel to the transepicondylar axis of a human femur based on the location of the anteroposterior femoral axis.
Establishing proper femoral component rotation is critical to the success of knee replacement surgery. There are a variety of anatomic landmarks that are used intraoperatively by the surgeon to ascertain the proper rotation and include the posterior femoral condyles, the transepicondylar axis and the anteroposterior femoral axis, or Whiteside's line.
The posterior condylar axis is frequently used as the reference for femoral component rotation; however, this landmark may be less accurate due to erosion from the arthritic process, particularly in the valgus knee.
The transepicondylar axis has been shown to be a reliable reference for placement of the femoral component in correct rotation; however, accurately determining the correct medial and lateral femoral epicondyles requires additional soft-tissue dissection. Also, the accuracy and reproducibility of defining the transepicondylar axis have been difficult to establish. See Stoeckl, Nogler, Krismer, Beimel, de la Barrera, & Kessler, Reliability of the Transepicondylar Axis as an Anatomical Landmark in Total Knee Arthroplasty, The Journal of Arthroplasty Vol. 21 No. 6 (2006).
The anteroposterior femoral axis of the femoral groove has been shown to be an accurate reference point for determining the correct femoral component rotation. A line perpendicular to the anteroposterior femoral axis has been shown to accurately indicate the transepicondylar axis and is even more accurate than the epicondylar axis in valgus knees for determining the correct femoral component rotation. For this reason, many surgeons use the anteroposterior femoral axis reference as the landmark of choice for determining femoral component rotation in total knee replacement surgery.
The anteroposterior femoral axis, or Whiteside's line, can be determined by the lowest point of the trochlear groove, or trochlear sulcus, and the anteroposterior point of the intercondylar notch. In other words, the anteroposterior femoral axis is a line drawn from the deepest part of the trochlear groove anteriorly to the center of the intercondylar notch posteriorly. The anteroposterior femoral axis, or Whiteside's line, can also be defined as a line through the deepest part of the patellar groove anteriorly and the center of the intercondylar notch posteriorly.
With emerging and popular minimally invasive surgical techniques in total knee replacement, the soft-tissue dissection required to accurately determine the transepicondylar axis is not practical. This requires the surgeon to rely solely on an accurate determination of the anteroposterior femoral axis to enact proper femoral component rotation. This axis is typically “eyeballed” by the operating surgeon with the use of marks made with an electrocautery device or a marking pen and then determining a perpendicular line to that free-hand. This method is inherently inaccurate, which prompted the present inventors to create a device and method that accurately, reproducibly and efficiently locates the anteroposterior femoral axis.